Because It's Convenient
by they're only words
Summary: Basically just a dark Dasey.  I realize the chapters are short, but that's just the way I write.  My first attempt at fanfiction, please R&R!  COMPLETE!
1. Chapter 1

A/N: This is my first story, so please be gentle with me. I've read a couple of dark Dasey stories, and I really liked them, so I figured I'd give it a shot. Reviews are appreciated, as are constructive criticisms. Flames, however, will be used to start a campfire for me to roast weenies over.

Disclaimer: I don't own Life With Derek, nor is any copyright infringment intended.

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Casey's POV:

Of course I only dated Sam to make Derek crazy. Why else would I want to be with him? Sure, he was sweet and nice and all that crap, but he was also boring as hell. The fact that it bugged Derek was the only reason to continue to do it. And I know that he only flirted with Emily to piss me off, so I would say that we are even. Of course, he doesn't see it that way, as I fucked Sam and he only ever made out with Emily. I told him, it's not my fault she's a prude, but of course, he wouldn't see it that way.

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Derek's POV:

Okay, so maybe I really did think that we should be even, but it was so much more fun to fuck with Casey. The fighting was so much more fun than just agreeing with whatever she said. So I'd fuck random girls, she'd get pissed, we'd scream, she'd find Sam and fool around with him, and then we'd end up in my room. Again. Every goddamn time.

"Fuck you, Derek! What was the slut's name, hmm? Did you even bother to find out?" Casey screamed at him.

"Why should I find out? Does it really matter? We both know I just do it to fuck with you." Derek replied nonchalantly.

"Thank you, Derek, for reminding me that you're such an asshole. I hate you."

"I know. Don't forget this goes both ways."

"Fuck off. I'm not coming back this time."

"Yeah, you will. Right after you get back from Sam's house. You'll come back because you need a good fuck after you get all hot and bothered, and let's face it, Sam just doesn't do it for you, and he never did."

"Maybe that's just what I tell you, so that you'll feel better about yourself."

"If that were true, you wouldn't bother coming back. You'd stay with the nice guy. You only come back to me because I'm a good fuck."

"I swear, I'm not coming back." She walked out and wished it was earlier so that she could slam the door.

"Yeah, you are. You always do." He laid down on his bed and waited for her.


	2. Chapter 2

Disclaimer: I don't own this show, and every night I cry about it.

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Casey climbed out her bedroom window and shimmied down the drainpipe. She didn't even have to think about what she was doing, she had done it so many times before. She pulled out her cell phone and sent a text message to Sam to let him know she was on her way.

"God, he's such an ass. I don't know how I got sucked into this sick cycle. It's absolutely ridiculous. It's true, I am just using him for the sex. If only Sam was better, I could just stay with him."

That was the good thing about Sam. He was a guy, and therefore always willing to have sex. Sam and Casey had maintained a friends with benefits relationship ever since the breakup, with Sam never asking questions as to why she showed up in the middle of the night all the time.

Sam's room was on the first floor. Casey knocked on the window. Sam shuffled over and opened it.

"I dunno, Casey. I'm kinda tired."

She kissed him hard, angrily.

"And now I'm awake."

She pushed him onto the bed and climbed on top of him. She kissed him again, and he kissed her back, trying to be gentle, not picking up on her violent vibe, just like he never did. He ran his hands up her sides gently, while she tore his pajamas off of him. He was taking too long with her clothes, so she sat up and took them off herself. She reached into his nightstand and helped herself to the box of condoms she knew was there and put one on him.

"Casey, are you sure?"

"Shut up Sam."

She slid herself down onto him. She began to move, gyrating her hips in just the right way. She began to move faster, and then, before she knew what happened, Sam was done.

"Really, that's it? God, you disgust me. You're so bad at this."

"I know. I'm really sorry Casey. It's just that I'm really tired, and kinda stressed about our test tomorrow in-"

"Shut up. It doesn't matter." She slid off of him and began to get dressed.

"You don't have to go yet Casey. You could stay for a little bit." He pleaded with his eyes. She knew he wasn't really over her. He was happy to be friends with benefits, because he really just wanted to be with her in any capacity he could.

"No, you're tired. I'm going home now so you can rest." She climbed out his window and began the walk home, knowing that she was going to have to go to Derek now, just for a little satisfaction.


	3. Chapter 3

Disclaimer: Still don't own it. Makes me sad, but hey, what can you do?

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Derek thought about his night. He had been on a date with a girl, Marley, or maybe Carley. It was hard to tell. It really didn't matter, the point was that she was blonde, big breasted, and easy. And it made Casey insane. He could tell from the look on her face when Marly/Carly showed up at their house earlier. And then, later, when he snuck her up to his room. Naturally, he had her moaning before he even entered her, and the entire time he fucked her he could see Casey's face, making that narrow look she gets when she's pissed off. He did feel a little bad for fucking these girls just to piss Casey off, but then he thought about the pleasure they got from it, and figured it didn't matter.

Casey climbed through her window and shut it. She took of her shoes and socks, and then figured, "to hell with it, might as well make it quicker" and took off all of her clothes too. She walked across the hall to Derek's room and walked through the door. She didn't even bother knocking.

"Yep, about 11 minutes. Five minutes there, one minutes of fucking, and five minutes home. Sam sucks."

"Fuck you, Derek. At least Sam has feelings." Casey spat at him.

Derek leaped off of his bed, grabbed her shoulders, and said, "Fuck you right back, Casey. I have feelings, it's not like it's my fault that whenever you're around they're feelings of nausea."

"You seem to be keeping your dinner down fairly well; maybe you're confused about the meaning of the word 'nausea'. It is a big word for you to use." She tried to push him away, but he grabbed her wrists. He kissed her, hard. She kissed him back, shoving her tongue in his mouth. The two of them battled for dominance, neither getting any further ahead of the other. He shifted her wrists into one hand and reached down to her breast with the other. She let a small moan escape her lips. She pulled his shirt off of him, and then his pants. He bent down and began to suck on her nipples. She moaned again, louder this time. He let go of her wrists and slipped two fingers inside of her. She bucked against him. He kissed her lips again, and then nibbled her earlobe. She reached down and began to stroke his member. Not wanting to wait for anymore invitation, he pushed her down onto his bed. He pulled a condom out of the package under his bed and rolled it on. He began to thrust into her. They were both moaning and moving in rhythm together. They both came at the same time. Derek rolled off of her and threw the condom away.

"I told you so. Sam can't please you like I can."

"Fuck you." Casey said, and then she left.


	4. Chapter 4

Disclaimer: Okay, so sick of writing this. I don't own this, obviously. If I did own it, I would be writing this stuff in scripts instead of posting it on the internet.

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At breakfast the next morning, there was tension in the room. Everyone else just chalked it up to the usual arguments between the two of them, which was basically what it was. The thing that no one else realized was that "the usual arguments" also included sex.

At school, Derek watched Casey flirt with guys, just as Casey watched Derek flirt with girls. When Derek saw Casey go into the boiler room with one of his teammates, he flinched a little, until Emily walked by.

"Hey Emily, how are you?"

"Oh, hi Derek! I'm fine, how are you?"

"I'm alright. What are you doing tonight?"

"Nothing. I mean, not because I don't have anything to do or anything like that, it's just that Casey has a date tonight, so, umm, I don't have anything to do, I guess. Wow, that sounded dumb, huh?"

"No, not at all." _So did. God, she's lame._ "Do you want to be doing something tonight? With me? Cause the house is going to be empty, for a number of various reasons, if you want to come over and hang out for a while."

"Yes! I mean, that'd be cool. You know, whatever. I could swing by. What time?"

"Eight."

"Okay, see you then."

Derek saw Casey coming out of the boiler room just then, wiping the corners of her mouth. He leaned in and kissed Emily, slipping in a little tongue at the last second.

Casey walked up to the two of them. "Ew, Emily, you don't know where he's been. Come on, I think I have some mouthwash in my locker."

"Nice to see you too, Casey. Probably wouldn't hurt for you to use a little of that mouthwash either, and I think you missed a spot, right here." He rubbed a spot on his lower lip, and then smirked at her. "See you later Emily."

"What does that mean, Em?" Casey demanded.

"He, uh, asked me to come over tonight. While everyone was out." She replied sheepishly, picking imaginary lint off of her shirt. Casey just glared at Derek's back, and took Emily to the bathroom to rinse, since she had been planning on doing it anyways, after the encounter with what's-his-bucket in the boiler room.

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"Derek, dude, your stepsister gives the world's best blowjobs."

"Sean, dickface, do you really think that is something that I would want to hear about my stepsister?" Derek replied, agitated.

"Sorry, but it's true. You could probably ask any of the guys in here, except for you."

_Oh, believe me, I know better than any of you._ "Is there any guy in here, besides me, who hasn't gotten some sort of sexual favor from my stepsister Casey?" All the guys looked around at each other, waiting to see if any of them would raise their hands. No one did. "Great, that's just great." Derek slammed his locker closed and went out to practice.


	5. Chapter 5

Disclaimer: I don't own Life With Derek, and my life is emptier than it should be as a result.

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He came home that afternoon pissed as hell. He walked straight up to Casey's room, walked inside, and locked the door behind him. He pulled her up from her spot on the bed, threw her against the wall, and kissed her, hard. He came up for air and said, "You slut."

"Oh, what's the matter? Locker room talks finally catch up to you? Cause girls talk in the locker room before gym class too. And I've heard plenty of things. Everyone seems to agree that you have the most dick control of all the guys, but all the other girls seem to think that you're too gentle. I don't know where they would get that idea. Do you take all your aggressions out on me, and then treat them gently? That's hardly fair. I can't imagine that you're any good when you're being gentle."

"Fuck you Case. I'm gentler with them because I know they'll talk about it. Yes, I do take all my aggressions out through sex with you, because you can't tell people that I'm vicious in bed. It's very convenient for me."

"That's all it is with me, isn't it? I'm here for you're convenience. Well, fuck you, because I deserve better than that."

"Oh, like you're not using me for the exact same reasons. It's convenient for you to fuck me after being out with Sam, or any other guy for that matter. If I didn't live right across the hall, we'd never have gotten together. Quit acting so innocent in this whole game, you're using me just as much as I'm using you. We both hate each other, this is nothing more than a good fuck."

"Fine, so maybe you're right. Doesn't make it sound any better." She walked downstairs and sat on the couch. Derek followed her.

"Why did you walk away? I was just getting warmed up." He pulled her up off of the couch and kissed her deeply. She sighed, and Derek forced his tongue into her mouth.

"Wait," she pushed him away. "We shouldn't be doing this downstairs. Someone could walk in at any time."

He pulled her back into him and kissed her again. "That makes it even more exciting doesn't it?" He kissed and nibbled on her neck. She moaned, and pressed herself into him. She could feel him getting harder already. He slid his hand under her skirt, and pushed her underwear down. He slipped two fingers inside of her, and she began to breath even heavier. He pulled his fingers out, and turned her over so she was bent over the couch. He pulled a condom out of his pocket, then pulled his pants and boxers down and put it on. He began thrusting into her, and she let out little moans with each thrust. As they were both nearing the end, the front door opened. George walked in carrying two bags of groceries, which he promptly dropped on the floor.

"What the hell are you two doing?" He yelled. They both scrambled to replace what little clothing had been removed. Casey tried to run for the stairs, but George stopped her. "I don't think so, Casey. You two are coming into the kitchen with me, where I can keep an eye on you until Nora gets home and we figure out what to do about this."

Casey said, "Fine, you can give us any punishment you want, but it's not going to stop us. You can't keep us under constant observation. Before too long we'll be adults and there won't be anything illegal about it. We're steps, there's nothing wrong with it."

"It's still not right. You two live together, you're treated like brother and sister." George replied.

"We may be treated like brother and sister now, but we didn't grow up that way. When two teenagers are thrown into a new living arrangement like this one, it's only natural that they begin to notice how attractive the other one is. Our hormones tell us to give it a try, since we're not really related." Casey responded.

"Yeah!" Derek said, not wanting to not contribute anything to the conversation.

George sighed and rubbed his hand over his face. "How long has this been going on?" He asked.

"About six months, give or take a couple of weeks." Derek replied, happy to be able to supply something of importance, finally.

"Well, it's going to stop now," George said angrily, "and Nora's not going to be happy about this either."

Casey responded, "You didn't know it was going on for the past six months, do you really think that you're going to be able to pay enough attention to keep it from happening now?"

"Yes, I do, because now we know that we have to watch you, whereas before, we thought we could trust you."

"Well, I guess we'll just see then, won't we?" Casey said smugly. Casey and Derek got up to leave.

"Oh, no you don't," George said, "you two are sitting right here where I can keep an eye on you until Nora gets home. I want you to tell her what you've been doing."

Derek said, "Okay, that's fine, but can I go to the bathroom real quick? This condom's starting to bug me."

"Fine, go. I'm glad to see that you two are at least being smart enough to use protection in your stupidity. I can't imagine how little brains your offspring would have."

After Derek had come back from the bathroom, him and Casey sat at the kitchen table while George made dinner. George would turn around to check on them every once in a while, but they weren't watched very carefully. Whenever George's back was turned, they would kiss each other, or pinch each other, and when George would look at them, Casey would kick Derek in the shins. As a result, the puzzle George had given them to keep them busy wasn't getting done very quickly.

Marti walked into the kitchen. "Smerek, come play with me!" She grabbed his hand and tried to pull him out of the chair.

"No, Marti, Smerek can't play right now. Him and Casey are in trouble and they have to wait right here." George told her.

"Why are they in trouble?"

"That's a good question. Were they fighting again? Because I thought we agreed not to mediate anymore unless they were doing bodily harm to each other." Nora walked in the door and set her keys down.

George replied, "Oh, believe me, this is a very good time to mediate. Marti, will you please go upstairs? Play with Lizzie or Edwin. We need to talk to Derek and Casey."

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A/N: Dun, dun, DUNNNN!! Oh, no, what's going to happen next? I'll post the next chapter when I have at least 5 reviews, so that I know that you guys are actually enjoying this.


	6. Chapter 6

A/N: Thank you guys so much for reviewing! I seriously appreciate it. This chapter was a little bit harder to write, just because I was unsure of Nora's reaction. Also, I spent a lot of time reading the new Harry Potter book this last weekend, and did nothing else as a result. I'm thinking that there will only be one more chapter after this. Let me know what you think!

Disclaimer: Still not mine. Still not making any money off of it.

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George looked at the two teens. "Well, is there anything you two would like to tell Nora?"

Derek looked back at him innocently. "No, not really. Why? Is there anything you'd like to tell Nora?"

"Derek! Shut up and tell her now!"

Derek looked at him questioningly. "How can I possibly do both?"

George gave him a look. Derek sighed. "Fine, fine. I'll tell her. Uh, Nora, Casey and I have been, uh, fooling around."

"Fooling around? As in…?"

Casey sighed. "Quit being such a big bunch of babies and just say it. Mom, Derek and I have been having sex for the last six months. We've used protection every time, we're not dating, we have no long term plans to be together, we still hate each other, and we're not going to stop."

Nora's mouth dropped open and she looked at her daughter. "Uh, you're joking, right?"

George answered for them. "No, she's not. I came home and caught them going at it in the living room."

"Casey, this is so unlike you. You're usually much more in control of your emotions."

"Mom, I'm still in control of my emotions. I still hate Derek. I don't want anything to do with him. When we have sex, it's purely physical. It's a release."

Nora stood there looking back and forth between Derek and Casey.

"Huh." She said, looking very confused.

"Huh!? That's all you have to say, huh? You find out that our children have been having sex for the past six months, and all you can say is huh?" George ranted at her.

"Well, I don't know what else to say, it's a little bit shocking, and I'm having some problems processing these thoughts." Nora just stood at the kitchen counter, looking back and forth between Derek and Casey.

"If you had seen what I saw, you'd have no problem believing it. It's pretty obvious that they're not making it up when Derek's got Casey bent over the couch with their drawers dropped." George continued to rant.

"Well, of course I didn't think that they were making it up, because that wouldn't make any sense. It's just kind of odd that they would be doing this." Nora said, calmly.

Casey looked at her for a second, then said, "Why is it odd? If it was Derek and another girl, or me and some other guy, you wouldn't think it's odd at all. The only reason you think it's odd is because you have been trying to make us into this twisted family unit, when it's obviously not going to work. Derek and I are just doing what our instincts tell us to do, if you hadn't forced us into this living arrangement we could do this without anyone freaking out."

"Well, Case, we are in this living arrangement, and we are trying to be a family, which is why what you two are doing is wrong." Nora said, finally catching up. Casey yelling at her brought her back to reality.

"No, it's not. It's not even illegal. It's only wrong because you think it's wrong. If you were more open-minded, then you wouldn't care." Casey said angrily.

Nora was about to say something back, when Casey stopped her. "Alright, it's obvious that we are never going to agree on this, so what if we just set some ground rules?"

"Okay, rule number one: You two can't have sex. Ever." George offered.

"Never mind, plan two: We discuss possible rules that we can all live with." Casey suggested, knowing it was better not to start another argument by telling them there was no way for them to stop now.

"Fine, then. What's your suggestion for rule one?" Nora asked skeptically.

"No sex in the house when other people are home." Casey offered diplomatically.

"Well, that won't work, because what if someone comes home and surprises you like I did today? We would really rather not expose Lizzie and Edwin to this, we don't want them to think that we condone this sort of behavior." George replied.

"Fine, then. No sex in the house period. We still have car privileges." Casey countered.

"Oh, but the car's not nearly as roomy. Can't we have, like, designated house time?" Derek pleaded.

"Derek, they're not killing us, and they're agreeing to not make us stop completely. I wouldn't push our luck." Casey cautioned them, as George and Nora just looked at them.

"Okay, that's cool. I can handle the car. Any other rules I'm going to have to try to work around?" Derek asked.

"Yeah, rules two and three: no one else finds out about this, and George and I forget we know anything. Unless things get serious, as in moving in together, getting pregnant, getting married, things of that nature, we don't want to know." Nora told them.

"Fine, those are the guidelines we were following anyways, so I think we can handle that." Casey stuck her hand out for a handshake and an official agreement. Casey and Nora shook, as did George and Derek, who both were glad that they didn't have to contribute much to the conversation.


	7. Chapter 7

A/N: Whoo-hoo, last chapter! Thanks again to everyone who reviewed, I really appreciate it!

Disclaimer: I don't own Life With Derek. I am starting to believe I'll survive without it though...

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Casey looked in the bathroom mirror, putting the finishing touches on her make-up.

"Getting all ready for the big date with Sam? Are you guys going to get back together now? Because if you did, it would be rather annoying for me." Derek stood just outside the bathroom, watching her.

It had been a little over a week since their talk with George and Nora, and they had been following the rules. However, no sex in the house had resulted in no sex, period, as they were both busy with hockey and dance. The only time they had any spare time to be together was at night, before bed. Casey had insisted that they follow the rules, seeing as how things could've been much worse.

"I sincerely doubt it, not that it would be any of your business if we did." Casey said to him without looking. As she turned to leave the bathroom, Derek grabbed her elbow and pulled her close.

"What about later tonight? This will be your first post-rules date. We both know you're going to need some action when you get home, and you're not going to want to go for a drive." Derek whispered in her ear and smirked.

"I'll be fine. I can wait until we can go for a drive. I, unlike you, have self-control."

"Come on, Casey, breaking the rules is a lot more fun than you think."

"That may be, but spending the next year in my room is hardly worth it. You're good, but you're not _that_ good." She pushed her way past him and walked downstairs to wait for Sam.

As she hit the bottom step, the doorbell rang. She opened the door to find Sam standing on the doorstep. "Good timing," she said appreciatively. "Bye Mom, bye George, I'll be back later."

"Bye Casey, be safe, have fun." Nora called back to her from the kitchen.

Sam and Casey walked out the front door and headed to his car. "So, what do you want to do tonight? I thought maybe we could get dinner and then catch a movie, or something. It really doesn't matter to me, I could do anything." Sam said nervously.

Casey smiled at him. _It really is too bad he's shit in bed, because he's adorable._ "Whatever you want to do is fine."

"Okay," Sam replied, as he walked around to help her with her door.

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Sam parked the car in his driveway. "Are you sure you want to sneak up now? We could just wait a little bit longer, until my parents are for sure asleep."

"Sam, I thought you said that they usually went to bed at 10:30." Casey said impatiently.

"Well, yeah, but maybe they're not fully asleep yet." He replied, looking uneasily up at the house.

"Sam, it's a quarter to midnight. They're asleep. Now, go to your room, and open the window so I can get in." She pushed him out of the car.

"Fine," he grumbled, as he slowly got out of the car and walked, even slower, up the path to his front door.

Casey waited for the light in his bedroom to come on before she got out of the car. She climbed in through his window and kissed him.

Sam pulled away from her and went to turn off the light. Then he sat on his bed. Casey went to sit next to him, then leaned in to kiss him again. He responded, parting his lips to allow her tongue in his mouth. She reached down and set her hand on his knee, then began to slowly move it up. When she reached his groin, he let out a soft moan. She could feel him getting harder. He ran his hands up her sides, and began fondling her breasts through her shirt. She began to unbuckle his belt, and he abruptly pulled back from her.

"Casey, is this going to end the same as it always does?" He questioned her demandingly.

"What do you mean?" She asked without moving her hand away from his buckle.

"Do you want a relationship, or is this just sex for you? I'd really like a straight answer, because I'm sick of getting jerked around."

"I thought you liked being jerked," she teased.

"You know what I mean," he said as he pulled her hand away and set it in her lap.

"God, Sam, when did you become the girl in this scenario? I thought teenage boys just wanted sex, and if there were no strings attached, well, then, even better."

"Guys have feelings too. Just because most of the male population are Neanderthals, doesn't mean that all of us are. I like you, Casey, and I can't keep doing this if there's no hope for anything other than a purely physical relationship between us."

"Well, I'm not really in a good place for a relationship right now. I just kind of want to focus on my schoolwork. I'm sorry Sam, if you don't want to do this, then I guess I'll go." She began to leave.

"Wait, you don't have to go just yet. Okay, fine, you don't want a relationship. But, you're already here, so why not just finish what we started, and then quit after tonight?"

"See, you are really a guy, you just can't pass up on the offer of sex." She pushed him down onto his bed and climbed on top of him. She kissed him again, and reached down for his buckle again, this time succeeding in getting it off of him. She unzipped his pants, and pulled them and his boxers down to his ankles. She hiked up her skirt and pulled her underwear off from underneath it. He pulled a condom out from his night table and slipped it on. She settled herself down on his member, and began to move. Sam let out a soft moan, and then let everything out.

"Goddamn it!" She swore, climbing off of him. "I don't know why I even do this, it's not even worth the risk of getting busted by your parents." She put her underwear back on, then headed for the window.

"Casey, wait, I'm sorry," he pleaded at her back.

"Why should I wait? You can't," she said as she climbed outside.

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Casey walked inside, and headed upstairs to her room. She went inside, set her purse down, and sat down on the bed for no more than thirty seconds. "Damn it," she muttered, as she walked across the hall to Derek's room.

"I knew you'd come back. You always do." He said as she walked into his room. She could tell from his voice that the dammed smirk was on his face.

"Fuck you, Derek. You're such an asshole," she said in a tired voice.

"I know," he whispered as he reached up her skirt. "I know."


End file.
